Tsunami warning: Waiting on siren sound may cause deadly delay

Civil Defence is being urged to quickly improve its coastal warning systems. But could these systems actually save us? And do scientists know enough about tsunamis? Science reporter Jamie Morton investigates.

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Every time Steve Morris takes his two young daughters to the local beach, signs of tsunami danger surround him.

The Tauranga father wonders how the grassy sand hills that drop down from Papamoa Domain were once formed; he hopes they'd provide a big enough buffer to stop a tsunami if a large one ever swept upon the densely-housed strip of golden beach that runs 20km to Mt Maunganui.

An inundation map, assuming a 6.7m high wave, puts his three bedroom brick-and-tile house, exactly 1000m from the beach, just out of reach.

Things are more frightening under another scenario unveiled by the Bay of Plenty Regional Council last month.

This has a 13m-high wave, thrown up by a massive quake in the Kermadec Trench, bearing down upon the seaside holiday spot at night time with just 50 minutes' warning.

More than 900 Papamoa residents are wiped out, erasing around 6 per cent of the local community.

Damage to nearly 1500 local homes leaves a damage bill of $54 million.

Mr Morris, acting chair of the Papamoa Progressive Association, has been researching local natural hazards while battling the city council to get louder warning sirens installed.

Worries among locals had grown with three major tsunamis - Japan, Samoa, and 2004's Boxing Day tsunami - causing widespread death and destruction and all striking within the last decade.

"If something were to happen here at night when everyone had their communications devices switched off, you have the potential for large-scale loss of life," Mr Morris said.

While the council has been looking at small electronic sirens along the coastline, Mr Morris' group has been fighting for something a little more old-fashioned - bulky WWII-style air raid sirens.

Despite the debate, both Mr Morris and the city's mayor, Stuart Crosby, remain convinced that New Zealand needs one uniform tsunami warning system, and quickly.

Mr Crosby has written to Civil Defence urging them to improve warning systems, which vary by region.

"I think Civil Defence needs to progress very quickly a national tsunami warning system that everyone in the risk area can become familiar with, and that local authorities like ours can move to implement over a period of time," Mr Crosby said.

"Our research has shown us that there are various systems up and down New Zealand, from your traditional fire station sirens, through to electronic-type devices.

"As we are a very mobile community, particularly in our summer holidays, that could present confusion for both full-time residents and visitors to coastal regions."

Mr Crosby added that sirens should be part of a package of tsunami response planning, ranging from evacuation plans to public awareness.

Auckland's electronic sirens, tested yesterday, are spread in the north from Point Wells to Waiwera and in the west from Bethells Beach to Herald Island, but they differ from air-raid type sirens found in centres such as Napier, Timaru, Lower Hutt and the Eastern Bay of Plenty.

Civil Defence operations manager David Coetzee agrees with the call for a single tone, yet he and his agency don't support the concept of tsunami sirens anyway.

Mr Coetzee explained that, in a "distant-source" tsunami, perhaps generated by a far-away quake in South America, authorities would have ample time, even more than 12 hours in cases, to evacuate coastlines.

But in the worst-case scenario of a near-source tsunami close to home, delivering a destructive torrent in a matter of minutes, the last thing planners wanted was for people to wait for a siren sound.

This type of tsunami, as the Japanese saw two years ago, would likely provide its own warning system - a thunderous and long-lasting ground shake.

"There is only one best way - and that is ourselves feeling the earthquake and responding to that," Mr Coetzee said.

"So it's a matter of public education to prevent the complacency ... and let the public understand what a siren can do and can't do."

Hundreds in Japan paid for complacency with their lives in the wake of the Tohoku Earthquake on March 11, 2011.

"Even when sirens did go off, they didn't see anything happening, or in other places they waited for the siren, but the siren sound was too late - so they couldn't escape the thing in the end," Mr Coetzee said.

"And the mere size of the quake knocked some sirens out, so people were waiting for sirens that were never going to sound because the infrastructure that supported them got disabled."

Ultra-loud tsunami sirens favoured by Mr Morris' group might also prompt evacuations in inland areas out of harm's way, he said.

"And if you come up with a standard, where does that leave the councils that already have sirens they've invested in?"

Auckland Council is in just such a position. Left with a cluster of sirens from previous councils, city civil defence planners are reviewing technology to ensure the next generation of systems is as advanced as possible.

No sirens are being installed around the city at the moment.

Auckland Civil Defence has meanwhile launched a messaging system, freely downloadable to smartphone handsets, which Aucklanders could use to be notified in the event of impending natural disasters.

But group controller Clive Manley reaffirmed people should not rely on authorities for flash-fire tsunamis.

"The message we do give to the public is that when it's a close-source event, they should be looking for their own signs," he said. "If they feel an earthquake and they are close to the coast, then once the quake has stopped, they should go to higher ground."

At some of New Zealand's more dangerously exposed areas the window between a quake and a tsunami reaching the shore might only be 20 minutes.

Mr Coetzee said while national response systems would still be activated, they might come too late for those in the line of fire.

"From a national level, we may get our stuff out within the 20-minute timeframe, but the local guys must still activate their local warning systems."

These issues aside, he admitted Civil Defence could do much more to at least push public awareness.

A pilot survey in Wellington this summer found as little as 7 per cent of local people realised they were not going to get an official warning for a local-source tsunami which could sweep through the city just 12 minutes after the shaking stopped.

"And I think we can do more in providing for vertical evacuation capacity, which is an area that New Zealanders have not really gone into, but has saved hundreds of thousands of lives in the Japan scenario."

In Japan, pedestrians walked by these high and sturdy tsunami-safe buildings and structures every day, so became familiar with signs highlighting them as evacuation points. External staircases fixed to the sides allowed people to safely reach roof areas. In the 2011 disaster, however, man-made evacuation sites had not always been high enough to escape the surges that engulfed Japan's coasts.

The Japan disaster and the 2004 Boxing Day tsunami have also rewritten much of the science of tsunamis and the faults that trigger them. Both catastrophes began from subduction zones that were commonly believed not capable of generating huge earthquakes.

"All of the scientists who study these faults have now gone back to the drawing board after those events," said tsunami mapping scientist Graham Leonard, who travelled to Japan after the 2011 event and came upon some alarming findings.

Japan was the only country to have spent millions on an earthquake detection system that would enable authorities to pick one of 100,000 scenarios to gauge the wave height of an incoming tsunami.

Yet the wave height they calculated was a massive under-estimate - what was forecasted as a wave a few metres high turned out to be more than 10m, killing many who had chosen not to evacuate.

Given these flaws, New Zealand and other nations have looked away from spending large sums on such systems.

"And we heard from several of the emergency managers that people thought it was just another false alarm, even though they had just felt a three minute-long quake," Mr Leonard said. "They would never have felt an earthquake anywhere as long as that in their lives, yet they heard the sirens going off again and thought, 'Oh, well that's another false alarm', so we were really quite distressed by that."

Among the ripples that reached New Zealand is a soon-to-be-released update of GNS Science's comprehensive 2005 report Tsunami Hazard and Risk in New Zealand.

"They have said we don't have a strong way to say if any subduction zone won't have a big one - so at the moment we have to assume that they all can."

Despite this, our scientists could still effectively forecast the size of a distant-source tsunami after it was generated and before it arrived, said tsunami expert Dr Jose Borrero, a senior marine consultant with eCoast Ltd.

"I would say we'd know pretty quick and would have some good end-numbers to work from, but that's not to say you can't always do more or refine things."

A tsunami from a far-field event would likely be a protracted event, with the largest wave coming several hours after the first wave arrived.

But ultimately, the alternative local-source tsunami would always prove the more menacing possibility.

"The problem with these things is that they are so big that there are simply scenarios you can't plan for," he said.

"If you were actually going to plan for that, no one would be allowed to live at the beach.

"And we don't know if that's going to happen in 15,000 years or if that's going to happen tomorrow."